The present invention relates to a vehicle control device, in particular for agricultural vehicles, such as tractors.
More specifically, the present invention relates to a device for controlling a clutch for transmitting torque to a power take-off of an agricultural vehicle, e.g. a farm tractor, to which the following description refers purely by way of example, in that, as will be clear to and expert in the field, the control device according to the present invention may be used for activating any type of actuator or for initiating any type of operation.
Agricultural vehicles are normally equipped with a power take-off, which is activated or deactivated by a clutch in turn engaged or released by means of a control device.
In Italian Patent Application BO98A000121, for example, a clutch is controlled by a lever movable by the user from a rest to an engaged position, and which is guided along a slot having two circular holes of different diameters corresponding to the rest and engaged positions. More specifically, the rest position hole is larger in diameter than that of the engaged position; and the lever has a locking member stressed by elastic means and comprising a first cylindrical portion, which engages the rest position hole, and a second truncated-cone-shaped portion, which, in the engaged position, is automatically engaged inside the engaged position hole by the elastic means. To switch from the rest to the engaged position, the locking member must be raised by the user to move the lever, and can be released by the user along the slot, even before reaching the engaged position, in which case, the elastic means slide the locking member along the slot and automatically into the engaged position.
Though an improvement on existing devices at the time, actual use of the above control device has revealed several drawbacks which may be eliminated by the control device according to the present invention.
More specifically, the major drawbacks detected in the control device described in Italian Patent application BO98A000121 are the following:
(a) full clutch engagement can only be ensured by allowing the lever a travel angle in excess of normal, to allow for yield of the flexible cable and other members;
(b) poor sensitivity of the lever, during engagement, on account of the sliding friction to which this type of control device is subject; and
(c) severe stress on the lever when releasing the clutch, if the user fails to simultaneously release the truncated-cone-shaped portion of the locking member from the engaged position hole; such stress may even result in breakage of the cable, and is uncontrollable by depending largely on the friction between the truncated-cone-shaped portion and engaged position hole.
Accordingly, it would be desirable to provide a clutch mechanism that overcomes these know disadvantages of the prior art.
It is an object of the present invention to provide a vehicle control device, in particular for agricultural vehicles, that overcomes the aforementioned disadvantages of the prior art.
According to the present invention, there is provided a vehicle control device, in particular for agricultural vehicles; the device comprising a control lever, and guide means in which the lever is movable by a user from a first rest position to a second engaged position; and the device being characterized in that the lever is also subjected to the action of elastic means for moving the lever into the first rest position if the lever is released by the user before reaching a given point along the guide means; the elastic means also moving the lever into the second engaged position if the lever is released by the user past said given point.
A first major characteristic of the control device according to the present invention is that, by varying the geometry of certain components of the device, it is possible to change both the initial intensity of the resisting moment exerted by the guide, and the law by which said resisting moment varies along the path traveled by the lever between a first rest position and a second engaged position. Adopting a particular guide geometry, the resisting moment of the guide may, if necessary, be maintained substantially constant over the entire angular travel of the control lever.
The user""s hand thus becomes sensitive to the mechanical action taking place on the clutch. That is, the resistance of the clutch is, as it were, transmitted instant by instant to the hand of the user, who thus has complete control over engagement of the clutch.
A second major characteristic of the control device is the reduction, in use, of the natural spontaneous rotation stability range of the lever, which stability is mainly due to the friction between the lever and the guide means guiding the lever along a given path. Using an idle roller on the lever and in purely rolling contact with the guide, it is possible to so reduce friction that, if, for any reason, the lever is released by the user before reaching a given point along its path, the lever is forced by the moments involved to return to the rest position. Conversely, if released by the user past said given point along its path, the lever moves spontaneously to a final point of equilibrium, at which the user is certain the control, e.g. a power take-off clutch, is fully engaged.
The action of a spring keeps the roller pressed at all times against the contoured portion of the path, so that forces are generated depending on the slope of a ramp and which assist the rolling movement of the roller just before and just after a given point along its path.
The control device according to the present invention may be used, for example, in the hydraulic power-assist device described in Italian Patent Application BO98A000121, the content of which is considered an integral part of this disclosure. Being a tracking type, the hydraulic circuit of the device described and claimed in Italian Patent Application BO98A000121 provides for accurately and safely modulating engagement of the clutch. When activating the device according to the present invention, the user has the impression of being able to modulate engagement of the clutch effortlessly as required; and, the idle roller on the lever practically eliminates any possibility of jamming along the guided path between the rest and engaged position. As already stated, in the event the lever is released by the user, for any reason, before the clutch is fully engaged, the device according to the invention provides for restoring the lever spontaneously to the rest position, thus preventing possible damage to the clutch.
Once the engaged position is reached and the user""s hand releases the lever, the device according to the invention ensures the engaged position is maintained by allowing a certain amount of scope to accommodate any timing errors of the levers, any setting errors, or any increases in length due to settling of the flexible cable connecting the lever to the hydraulic part of the device.
Moreover, when the user turns off the engine, the hydraulic circuit pressure is also cut off, so that, if the power take-off is connected, the return load of the cable increases, thus producing a destabilizing moment greater than the stabilizing engagement moment, so that the lever is restored to the initial rest position in exactly the same way as in the device described in Italian Patent Application BO98A000121.
Moreover, in the rest position, the lever advantageously engages a lateral cavity to prevent accidental engagement of the clutch.
These and other objects, features and advantages are accomplished according to the instant invention by providing a vehicle control device, in particular a clutch mechanism for a tractor, that includes a control lever and guide mechanism in which the lever is selectively movable from a first rest position to a second engaged position. The control lever is subjected to the action of an elastic apparatus operable to move the lever into the first rest position if the lever is released before reaching a given point along the guide mechanism. The elastic apparatus also being operable to move the control lever into the second engaged position if the control lever is released past the given point.